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Lack of fusion (LOF) in inclined downhill MAG welding — a study of the phenomenon and practical recommendations in order to avoid LOF

Peter Nerman, Johan Andersson, Erik Tolf

Abstract

In order to avoid LOF in downhill inclined two pass MIG/MAG-welding it is therefore preferable to weld in the smallest possible downhill inclining angle, not to use too highwire feed speed/travel speed ratio and to use a combination of arc type, shielding gas and filler type that gives an advantageous penetration profile. Filler type/shielding gas combinations that gave successful results in this work (low occurrence of LOF) are metalcored wires and ∅1,6 mm solid wires combined with shielding gas mixtures containing Ar+30%He +8%CO2 or Ar+20%CO2.

It is however not possible to give exact recommendations on inclining angles and wire feedspeed/travel speed ratio since these variables will probably be strongly dependent on the welding situation. When welding is going to be performed in situations where an increased risk for LOF can be expected it is therefore recommended to perform a procedure test. LOF caused by advancing weld metal have a very typical appearance, which easily can be recognised on a well prepared macrograph. If LOF-defects occur in the procedure test the process conditions are unfavourable and must be altered in a way to avoid LOF (for example change of the wire feed speed/travel speed ratio to a lower value).

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Senast ändrad av: Peter Hjertsson
26 mars 2015

 


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